Ardonit, Montana and Fasonit slates are double-pressed flat fibre cement slates composed of Portland cement, high-quality organic fibres, mineral aggregates and water.

Within the Ardonit, Fasonit and Montana range, SVK offers both non-pre-punched and pre-punched slates, the latter for certain formats and for the most common enclosures (for more information, consult our brochure).

For certain projects, however, the slates must be installed with a different enclosure and it is not possible to choose the pre-punched slates. In this case, the installer will therefore have to use non-pre-punched slates.

In this context, SVK carried out tests to check whether it is possible to nail slates without pre-drilling the holes.

A pneumatic nail gun was used to nail the slates to the battens. Calibration of the nail gun was done based on the findings after nailing the first slates and was then applied to the entire test stand. Nailing was done using stainless steel nails with a shaft diameter of 2.7 mm and a head of Ø8.5 mm. After installation, the slates were subjected to several durability tests and finally a visual inspection was also carried out.

During the inspection, it was found that some slates showed cracks at the edges and around the nails. It is assumed that this is partly due to the failure to perfectly calibrate the nail gun. Since the wood of the battens is a heterogeneous material that also contains imperfections such as weathers/knots, it is possible that some nails experience less resistance from the battens, increasing the impact of the nail head on the slate surface and causing micro cracks. In contrast, nails that encounter more resistance do not penetrate deep enough into the battens.

Another factor to consider is the dilation of fibre cement slates. Normally, the hole is drilled ± 1 mm larger than the diameter of the nail to allow for settlement of the slates. When nailing without pre-drilling, the diameter of the hole made in the slate is the same as the diameter of the nail. In this way, dilation is impeded leading to internal stresses in the slate.

Based on the above findings, SVK advises against nailing slates without pre-drilling. Before nailing, all holes should be pre-drilled with a diameter ± 1 mm larger than the diameter of the nails. The holes can be perforated or pre-drilled with a sharp drill suitable for fibre cement.